Today, semiconductor memories are widely used in main storage devices of large-scale computers, personal computers, home electric appliances, cellular phones, and the like. A NAND flash memory is a typical example of flash EEPROM non-volatile memories.
Examples of NAND flash memories include various kinds of memory cards such as an SD™ Card, an MMC card, an MS card, and a CF card, which are used as media for storing information about images, video, audio, games, and the like. In addition, NAND flash memories are also used as storage media for digital cameras, digital video camcorders, music devices such as MP3, and mobile personal computers, and are also used as storage media for digital television sets. Today, the production of these NAND flash memories increases in the market.
Flash EEPROM-type nonvolatile memories mainly include the NOR type and NAND type. In the NOR type, data are readable at a high rate and the number of reads is approximately 1013. The NOR type is used as an instruction code storage of a portable device. On the other hand, the NOR type has a small effective bandwidth at the time of writing data and is not suitable for file record or the like.
Compared with the NOR type, the NAND type may be integrated with a high-density. Although the access time of the NAND type is slower than the NOR type by 25 μs, the NAND type is capable of burst read and has a wide effective bandwidth.
Therefore, the data write time is 200 μs, and the data erase time is about 1 ms, which is slower than the NOR type. However, the NAND type may write and erase a larger number of bits of data at a time. Therefore, with the NAND type, data are fetched in a burst mode and data may be written in units of pages. That is, the NAND type is a memory with a high effective bandwidth and is used as a memory card and a USB memory, and is recently used as a memory of a mobile phone.
In a NAND-type flash memory, a high voltage of about 20V is used to write and erase data. Therefore, a high voltage is generated by a voltage generation circuit using a multi-stage charge circuit. However, the multi-stage charge circuit is a large-scale circuit, which occupies a large area. If an area of one charge circuit may be reduced, the overall size of area of the charge circuit may be reduced.